The present disclosure relates to a fixing device fixing a toner image, which is formed on a recording paper, onto the recording paper and an image forming apparatus including the fixing device.
An image forming apparatus, such as a copying machine, a printer, a facsimile and a multifunction peripheral having each function of these devices, including an electrophotographic printing mechanism is provided with a fixing device. The fixing device includes a heating roller having a surface heated by a heat source and a pressuring roller having a rotation shaft arranged in parallel with a rotation shaft of the heating roller. When a sheet having a surface, on which a toner image is formed, is passed through the fixing device, the sheet is sandwiched between the heating roller and pressuring roller by a predetermined pressure and heated. Thereby, a toner is molten to the sheet and an image is fixed onto the sheet.
This kind of fixing device generally includes a temperature detecting element, such as a thermistor detecting circumference face temperature of the heating roller, and a temperature adjusting element, such as a thermal cut adjusting supply and interruption of electric power to a heater built in the heating roller. These elements are used to control the circumference face temperature of the heating roller.
The fixing device may include an exterior case made by synthetic resins. The exterior case has a first casing holding the heating roller and a second casing holding the pressuring roller. The temperature detecting element may be arranged at a predetermined position on an inner wall face in a situation of facing to a circumference face of the heating roller at a prescribed distance.
However, the exterior case is made by synthetic resins as mentioned above. Because of this, the exterior case, particularly the first casing holding the heating roller, may be deformed by receiving heat generated from the heating roller. When the first casing is deformed, the distance between the temperature detecting element arranged in the first casing and the circumference face of the heating roller is varied. In order to suitably control the circumference face temperature of the heating roller, the distance between the temperature detecting element and heating roller is important. However, if the distance is varied as mentioned above, the circumference face temperature of the heating roller cannot correctly be detected. As a result, it is impossible to suitably control the circumference face temperature of the heating roller.